Too late?

I'm old enough to have been around the block a couple of times by now. I've fallen in and out of love more than once and I'm starting to wonder if I'll ever find someone I'd be happy with.
No one can forget their first love because the first one is usually new and untainted by past experience. The longer you live, the more people you meet, and the more things happen to you the harder it is to love anyone unconditionally.
My new girlfriend had a long and serious and very intimate relationship with a man. Each time we touch, I can't help but wonder if he did the same things to her, and whether she's thinking of him when we're together. There's no reason for this except my stupid manly paranoia, but still it's there.
It kills me to be so immature about it. I have never felt this way before. I have never given a crap about a woman's past until now. I don't know if this is what love is, but it's tearing me apart.
I don't know if i really like it, but I know for a fact that I can't/don't want to live without her.
People always sold that BS about how, "if you love someone you'll let them go, and if the come back they really love you back."
I beg to disagree now.
If you love someone, you hold onto them, and fight for them, and do whatever you need to do to keep that person next to. Love is about sacrifice, and sacrifice is about pain. If you really love someone, you should be willing to hurt for them, and that is the lesson I'm learning now.
Each time I think of her and my heart aches, each time I see any evidence of her with her ex-bf and my body freezes up, it's love killing me little at a time.

Rumi was right when he said, "Love is a slaughterhouse."

I believe it would be best for you to come to terms with the fact that your girlfriend dated someone before you. In the modern world, it is not usual for women to date multiple men before getting married. As long as she isn't pining over her old flame, you should be confident that she wants to be with you now. Jealousy will just eat you up and will eventually cause you to lose the person you say you don't want to be without.