I may be single for the rest of my life

I've (24m) only had one relationship since I've moved out on my own when I was 19 in 2011. I broke up with her after 3 months, I can't remember why. But ever since. I've found it increasingly difficult to build friendships/relationships with women. I do have girl friends of course, but a relationship in any sense just hasn't been in the stars for me. I've never dated anyone longer than a year. I'm fairly inexperienced I guess when it comes to relationships and I feel like I'm missing out while it seems like everyone around go through relationships fairly often.