how to go from foreplay to sex?

I have no problem initiating foreplay and getting my girlfriend in the mood, but I never seem to know when to move on to sex. I've always had this problem with sex, not just with my current gf. We either end up making out with petting for a long time, or we strip each other and give manual stimulation.

It's weird because I can get her off easily without penetration at all sometimes just dry humping does the trick, and she can get me off no problem, but I feel like an ultimate failure every time we are together because we didn't go all the way. I feel like she expects me to know when to stick it, but is disappointed because I never do. I feel like we have lesbian sex because I don't know when to, or even use my man parts at all. I guess if you think about it, I'm the one disappointed in myself for being inadequate.

I know this is a conversation I should be having with her, but I want to impress/surprise her.

The specific part I get stuck on is after we have been making out, I've rubbed her down, and she's bothered and ready, I freeze up because I don't have a condom on so I roll over next to her and use my hand instead. I don't want to just get up out of bed, go put a condom on, and return. it doesn't feel smooth enough for me. So if there was a way to make a smooth transition between the two I would be set.