Why is it difficult for me to get and maintain erections sometimes??

So this is probably gonna be a long thread, but anyways....

So to start off I'm an 18 almost 19 year old male. I am bisexual, leaning towards the gay side. I am in the closet and plan to never come out. Usually when I masterbate it's to gay thoughts. But anyways I was a virgin until about 2 weeks ago. Had sex with a girl. We are still fucking. But the problem is, I sometimes have trouble with my erections. I feel like the only thing that turns me on is the fact that I'm havin my dick rubbed. Not that I'm with a woman.

Now I googled it and aparently most guys get turned on from just making out. I don't get turned on unless she's touching me all over. And even then it's hard. Like there has been 2 times so far when sex failed cuz I couldn't get it up or failed to keep it up. And half the time when we are fuckin I feel like I'm not even fully hard. And we had sex earlier today. At first when she came over I was very turned on from just being in bed and cuddling her touching me. But sex didn't happen for another hour. By the time it did happen she started stroking my cock and I was having trouble getting up. So she had to go down on me to get me up.

Sometimes when she comes over and I get turned on I feel like I have to have sex right away cuz otherwise I might not be able to get up if we wait a bit. How can I change this? Like one time I got up, and by the time I got the condom on I was soft. Why is this?

Is it becuz I'm just not atracted to her. Am I just 100% gay? This sucks cuz it makes me afraid to have sex. Like she's textig me to come over and fuck right now. But I'm makin an excuse cuz I'm afraid this might be one of those times where I can't get up. It sucks. Like I'm always trying to avoid having sex cuz of this issue.

Should I try Viagra or something? I mean I can literally have her naked squeezing her tits and not be turned on. And apparently most guys are turned on just from kissing? Only stimulation turns me on. Is this just showing me that I'm really gay and not bisexual?? I mean I dnt think I am. I kinda developed a minor crush on a girl earlier this year

What should I do? Should I try sex with a guy and see how easily I get turned on?? Maybe one of those gay chat sites??

What should I do? Viagra?