If you're not ready, don't do it. Simple as that.
Any guy who would be even remotely o.k. with the idea that you didn't actually *want* to have sex with him, let alone pressure you into it, is a serious creep and you deserve better. I know people talk a lot about 'oh guys always want sex, every guy pressures, blah blah...' but NO! That's not true at all! The good guys are the ones who respect you enough and care about you enough that the idea of pressuring you into something like that sickens them. That's how I knew I really did want my current boyfriend -it was abundantly clear that want I want and need is a priority for him.
Now, I don't believe that sex necessarily requires marriage, or even love -but, this varies widely by person, and I don't think anyone should do anything they're not 100% happy with -not just 'giving in' or allowing it to happen, but actively *wanting* it. If you're not sure that you want it, if you don't feel comfortable, then don't do it. If he can't respect that, dump his @ss. If you at some point in your life decide that sex doesn't require love for you, that's ok too -as long as everyone involved is 100% happy with what's going on, nobody feels pressured (and obviously, consenting adults using protection).
If you do decide to have sex, use protection -preferably two forms (hormonal birth control, i.e., the pill, shot, patch, etc., AND barrier method, i.e., internal or external [aka female or male] condoms), as hormonal birth control does diddly squat to prevent STI transmission and condoms are not as effective at preventing pregnancy (also, obviously make sure you're using everything correctly -they're only super-effective [99% effective at preventing pregnancy for the pill, 96-98% effective for condoms] when used perfectly, and sadly most people don't use them perfectly).
Bottom line: If you do, it's nothing to feel guilty about. But I suspect if you've waited this long there's a reason. You said it yourself, you're not ready, you're not comfortable. You shouldn't just be 'kinda o.k.' with having sex, you should WANT to have sex. If you don't, then don't do it! And if he's not ok with that, you deserve better anyway.