I'd advise you to get in touch with your own sexuality, or lack thereof, and take it from there
Yeah, I really think (from past posts, too) that you need to explore for yourself. Some men are just horrible in bed, and when you are young, you don't know any better. You think "Wow, sex is not that awesome and it's more like a chore." Been there, and done that. lol You lose interest in sex and think it's YOU, and since your BF can't get it up, I'm sure you're thinking to yourself "God...another chore to get him hard only for him to lose it...this sucks."
For me, once I found a great sex partner, I realized how awesome sex was. I've still dated men who were bad, and then I lost interest again. There are some men who are great in bed, very attentive, no problems getting it up, and will make you feel great.
I know this is probably harsh and I don't like to say "break up" to anyone, because there are so many factors, but I do not think anyone should get married at a really young age without experiencing good and bad sex. You wind up 5-10 years down the road really wondering what great sex is and you either A) stray or B) stay faithful and sexually repressed. That's not to say that some people are asexual and don't care about sex. That's not to say you can't be happy with a low sex drive and someone else who is not good in bed, but just because you're posting here and I've seen you ask a lot of questions about sex, you seem to have that desire to find good sex or at least find out what it's all about. I don't see anything wrong with this, but getting married can lead to some bad end results if you are married.
At 19, you're kinda in an idealist stage, but you turn 25, 26, 30 and you develop a very distinct personality and become sure of yourself and what you want. This might lead to hurting someone who you've grown away from, because you've matured and you KNOW what you want.