Castiel is cursed with a very specific gift: his charisma. This gift makes angels (and not only angels) stick to Cas even despite his express protests or his obvious incompetence as a leader. Creatures of various species follow him around like lost puppies; he cannot rid himself of lost souls begging for him to become their leader. He even grows on Crowley and their purely business dealings turn into something akin to "being each other's favorite enemy" . Castiel wins Gadreel loyalty in minutes, while the same angel was distrustful of Metatron, who excelled at making angels follow his lead.

There is another side of this gift. It's is a pussy magnet. You may like or not like Misha Collins portraying this character, nonetheless it is explicitly said that in SPN universum Castiel is insanely hot (which may be more than figurative, because apparently he is a Seraph - a being made of fire). There are pants dropping everywhere he goes. His conduct confirms it. Throughout seasons 4-10 he hooks up with 4 women (all right: a woman, a demon, a reaper and an angel). It looks like he can find a date within hours with one hand tied behind his back. He doesn't even have to lift a finger - women stick to him anyway. Why then does he stay single (and chaste - but I'm getting ahead of myself) for so long?

The answer is obvious when we take a closer look at timing.

As Emmanuel he marries a woman in season 7 (it was a pretty precipitous marriage - the timeline reveals that the spouses couldn't have known each other for more than 9 months). Then, as Crazy!Cas he has this murky, confusing relationship with Meg.

In season 9 Castiel has a one-night stand with a female reaper. One could argue that april seduced him in order to kill him, but she didn't really have to have sex with him. Human Castiel was homeless, hungry, lonely and dripping wet. She offered him shelter and food. It was quite enough to draw him into a trap. Sex was an entirely unplanned bonus she seemed to enjoy.

In season 10 the relationship between Castiel and Hanna develops to such an extent that even the man married to Hannah's vessel is in a way involved.

Why? Why are Castiel's romantic adventures limited to a period of a few months in season 7 and then burgeon in season 9 and 10? I believe it is because these were the only periods of time when Castiel was single.

In season 6 things get pretty rough between Dean and Cas which results in their first breakup. Castiel tries to make amends, but Dean refuses to accept his apology. Though heartbroken, Cas is free to have another partnrer.

Admittedly Emmanuel has no reservations against marrying Daphne because he does not remember who he really is and he obviously does not remember Dean. Later, however, Castiel remembers. He allows Meg closer because he realizes that Dean will not forgive him; that Dean is lost to him.

Then, he detects a note of forgiveness (and can't hold back an adorable grin) in Dean. Our favorite couple tries to get back together, which takes place in the Purgatory. In season 8 Naomi's intervention puts their newly regained trust in each other to the test; they fail and in break up for good. From then on Castiel is free to engage in relationships (or immoral misconduct) with whomever he wants.

There are two more things I'd like to analyze more carefully:

Castiel's virginity is the first of them. In the face of what I have just written it seems unbelievable that the angel remained a virgin for roughly 400 million years (in "The man who would be King" we learn that Castiel was an angel-child when first vertebrates crept out of the ocean; Ichtyostega - first "walking fish"- appears in the fossil record about 360 million years ago).

There is one explanation that is in accordance with Judeo-Christian lore and with SPN universum. Castiel says that angels are "here walking among you now for the first time in 2,000 years". From another episode we learn that an angel is a "multidimensional wavelength of celestial intent". Angels that are not possessing a vessel are bodiless. Castiel has not possessed a vessel for at least 2000 years. Perhaps inhabiting Jimmy's body is his first ride ever (infering from the fact that he has no clue how to treat a body - it takes him some time to grasp certain basic ideas such as combing hair or buttoning a shirt). We can safely assume that Castiel has spent the majority of his life as a bodiless, spiritual being. It is extremely difficult to imagine sex between multidimensional wavelengths of celestial intent, so indeed there was no occasion for Cas to be deflowered.

The second explanation of Castiel's nervousness when Dean asks about his sexual experience is much more interesting, though far less plausible.

Imagine a situation in which you:

- are in love with a person of the same gender

- you don't know if this person is attracted to people of the same gender, although he/she has been making innuendos suggesting that he/she might be bisexual or gay

- this person specifically asks about your sexual experience with opposite gender (Dean doesn't ask if Castiel has had sex' he asks if Cas has been with a woman)

Wouldn't you flush and nervously rub the back of your neck, then snap at the person, giving him/her a curt answer in order to end this embarrassing conversation in any way?

There is one scene supporting this explanation. When Castiel talks to Crowley about human sexuality, he does not seem embarrassed at all. Perhaps during his "last night on Earth" he was so funky not because of mentioning sex, but because it was Dean asking?c Perhaps Castiel suspected that Dean's question might have had a hidden agenda; That Dean was trying to spy out the land and indirectly ask if Cas was, by any chance, gay?

Castiel's relationship with Meg is the second interesting thread. In her last moments he refers to Castiel as her unicorn. It is a parallel to Sam's feelings for Amelia. The first layer of this parallel is, of course, the depth of Sam's feeling and Amelia's unavailability. They could never be together because of Sam's occupation... could they?

The subject of Sam's and Dean's inability to form a stable relationship will recur. Let me simply note that there are hunter couples or even hunter families. Of course Sam and Dean are in a specific situation (saving the world once a year on average does not allow for much downtime), but it is possible for a hunter to have a wife or at least try.

Moreover, Sam and Amelia try to get back together even after Dean's return from the Purgatory, when Sam gets back to hunting. It is not his occupation that finally tears them apart. It's Amelia's husband (that has been pronounced dead) returning.

So what exactly is an unicorn in this case? It is a person you deeply love; a person with whom you've had a brief romance; a person that is unavailable because his/her legitimate partner comes back and they try to work their relationship out.

It all adds up. Meg was in love with Castiel. They spent much time together when she was taking care of him in the mental ward. Later, when Dean and Cas get back together in the Purgatory, Meg has to give up on her beloved angel. As if it was not enough, Dean and Castiel get back from the dead (just like Amelia's husband got back from the dead) to top the parallel up. Castiel is Meg's unicorn: someone she loves; someone she can't have because he is in a turbulent, but long-term relationship with someone else.