I'm not sure what to believe...

So tonight my boyfriend said he was going to the hospital to see his friend that was in an accident. Now I fully believe that part of his story. Where I have my doubts starts when I go to the store which is across the street from the hospital. As I pull in I see him in the Chinese restaurant, which is fine, but then I see this girl's car waiting by the restaurant.

Now a little background about this girl. I've met her cause we all worked together at one point and she seems nice enough and she knows he lives with me. However he always seems to get rides with her and seems to text her a lot. He says it's about issues in her life or car issues she's having (he's a mechanic by trade) but it seems like more that could explain to me.

So as I continue she pulls around into a parking space. I park a few rows over in front of the store itself and I say this is sketchy so fuck it I'm calling his ass. I start off asking what he's doing seeing if he'll even say he's at the Chinese restaurant which he does. I then ask why she's there obviously waiting on him. He says he has no idea which I reply that the situation looks sketchy. He then say well fine I'm gonna go outside and ask her why she's here. The phone then goes dead silent I see him go out and talk to her and then she leaves. He then comes back claiming she just happened to see him there and her and her kid wanted to talk to him. When I asked about the phone going silent he says he didn't do anything and put it in his pocket with the speaker up but I didn't even hear pants rustling.

So at this point I'm thinking either

(1) he's telling the truth in which case she seems to have a odd relationship with him that seems inappropriate to me

(2) he did go to the hospital and asked for a ride home from her from the Chinese place but didn't want to admit it or planned to hang out with her after or

(3) he never went to the hospital and only left to hang out with her

I would just like to make it clear as well that I don't have an issue with him having female friends as most of mine are guys but he doesn't get why him seemingly being close to her and her daughter bothers me.

So what would you think in my situation?

Edit: I would just like to add that I was not intentionally spying on him. I was just going to the store for a few things and had no idea he was there. And I didn't wait to call him out cause I didn't think about it. And I have addressed that I'm not thrilled about his relationship with me and he asked me if I was jealous or threatened by her.