I think he bit him

I got a new cat on Sunday. He wasn't happy about it. He's 6 years old, 7 in April. He's been with his old family since he was 6 weeks, they felt they didn't have time for him. The first night was a disaster. He was upset, hostile and aggressive. I secluded him in a room which he didn't like, he howeled at the doors, scratche them and urinated on my daughters bed. So I opened the door and let him explore. My little Siamese followed us around, watching but not interfering until he but me while offering a treat. Leo, my Siamese, reacted immediately by puffing up and putting himself between us. He kept growling as I picked him up and put us in my room. He was then very needy, grooming me, yelling loudly and seekin attention. Since then he's been very hostile to Loki even though Loki has calmed and is being affectionate. I was petting Loki and noticed a swelled spot on his rear that is scanned over. I'm certain Leo bit him. I've been keeping them seperate for the most part but my husband thinks they need to "work it out" and let's them in the same room. The thing is that despite the fact I know they have come to blows I have seen them sleeping vey close to each other and they are constantly seeking each others company.
I have two questions. Does is sound like they can work out their issues despite the fights that have occurred and how should I treat the bite? We have such a fragile trust between us and I know that picking him up, fighting him into the carrier and going to the vet will shatter what little we've managed to build.