If she's too tense for you to insert your index finger, she's way too tight for PIV sex. If she can't relax enough for you to finger her, then she's either got some vaginismus going on, an obstructive hymen, or she's just really tense which is mental and emotional. She should see a doctor just in case it's one of the first two. I'd really recommend that you take PIV sex off the table for a while. Have lots of oral and manual sex. Make love without having intercourse. Learn what it takes to make her really turned on, to make her have an orgasm, or three. From the sound of things, you're fairly inexperienced with each other sexually so learning each other is a big step. Basically, have lots of "lesbian" sex. Once you understand how her body works, know it intimately with your hands and mouth and eyes, know what kinds of touches and pressures she likes, and even know how she's angled and shaped internally, and likewise, vice versa, her knowing your body as well, you can try and tackle PIV again with more success. Learn to feel sexy with each other. Sex is supposed to feel sexy. There is so much you can do without putting your penis in her vagina that will help you both get to know each other sexually and feel more comfortable with each other emotionally. Try to work through any barriers that are between you. Be naked together, touch each other everywhere, shower together, watch each other masturbate to learn what you each like, have oral and manual sex where the receiver instructs the giver on what they like and want, play with toys. If she likes her smaller dildos and is comfortable inserting them, have her insert it and play with it while you watch and then take over manipulating it for her. Once that's comfortable, try a larger one. Right now, it sounds like you don't know each other physically very well and you are also really feeling the pressure to make this PIV stuff work when you really need to just back off and get to know each other and yourselves a little better in this context. Work on doing all the little things that make you each feel sexy to yourselves and each other. Give her some money and let her go buy some sexy lingerie or clothes that make her feel sexy and then take them off with your mouth. Take her out to dinner while she's wearing some sexy underwear under her clothes, then go home and enjoy undressing her. Have a bubble bath together with some bubble bath stuff you both like and some candles, eat chocolate, better yet, eat chocolate off each other, drink wine or whatever you like to drink. Give each other massages. Be sexual with each other without actually having intercourse. Maybe read some sexy erotic stories or watch porn together if you both like those things. Send each other sexy text or voice mail messages, if you can do so without getting in trouble at work or what have you. Minus the pressure, add the sexy, and I bet you'll both be much happier and your sex life will improve. And NEVER underestimate the value of TALKING! Communicate, over-communicate. You can't communicate enough. Ask her how she's feeling, not just physically, about sex. Ask her what she thinks about. Ask her about her fantasies and what turns her on. Ask her what's going on in her head when you guys try and have sex and it doesn't work. My gf and I find that we like to have deep conversations in the bath together. Something about the intimacy of the bathtub with some candles and low lighting and a glass of wine, being naked together, holding each other in the water, lets both of us open up more freely. Anyway, main point is, relax, don't worry about the PIV stuff, get to know each other in every possible way, work through barriers, my guess is, the issue you're having will work itself out. If in doubt, seek out a therapist who specializes in sex and relationships.