A few other Beatle era songs could apply to this relationship too. For example 'In my life' they were possibly holding hands (I don't know how credible this is) John mainly wrote it but Paul helped write it too.
For 'I wanna hold your hand' they wrote it in a cramped room together.
A lot of Johns songs were autobiographical or semi autobiographical. One song he wrote was 'You've got to hide your love away' This could be about his marriage to Cynthia, or about Brian Epstein (who was openly gay) However I think that John probably wrote it about himself. The anthology version of this is lovely and you can hear John call Paul Macca in it :)
The song 'Here there and everywhere' was by Paul. Paul wrote it whilst John was sleeping by a pool, and he was waiting for him to wake up. It's a really nice love song and if you think that Paul was probably looking at John whilst he wrote it, then it gets a new perspective. It's also one of the only songs John actually complimented.
'Oh Darling' is interesting, if you don't think of the words Oh Darling it sounds like a Paul is singing Oh Johnny. Their relationship was crumbling at this point. To me it sounds like a sort of plea. "I'll never make it alone" could be talking about songwriting. In the anthology version John announces that Yoko's divorce had just gone through.
'Two of us' is a duet between John and Paul. I believe Paul said it started to be about John after his death. was meant to be about Linda, but some of the lyrics don't make sense if it is. Like the lyrics "You and I have memories longer than the road that stretches out ahead" Paul had only known Linda for 2 years at this point. Also, maybe I'm reaching but "the road that stretches out ahead" could be a direct reference to the song 'The long and winding road'