Issues with the first time sex with my girlfriend.

I was able to fully satisfy her with oral and some penetration but there were some issues. Keeping this short as possible. I've given and received oral with my ex but never inserted my penis. My girlfriend is tight and hasn't had sex in about 3 years. She wants me to be on top but I'm not used to that. I gave it a shot. The main problem is that I lost my erection after oral on her. And went I tried to put the condom on it just stayed soft unless she was to get on and grind on me. It made penetrating her hard because I was only halfway erected. The second thing with my half erected penis was that I found it hard to penetrate her from behind and it was basically hard to get inside from any position. But I'm sure it'd be easier fully erected. Last issue was that when I was inside, I couldn't feel much at all were as my girlfriend was orgasming. It felt like I wasn't all the way in but then again half erection. Also I doubt I wasn't gonna come. I'd appreciate any advise or comments. Does sex with a condom always feel like theres no feeling? Will I be able to come? I heard stress nervousness and anxiety prevent erections. I didn't tell her but I have a fear of my condom failing. How can I get past this fear, relax, and have a throbbing erection to get inside her? Thanks plenty.