How do I get over my worries about my boyfriend?

I’ve been with my boyfriend now for about 5 months. We’re both on the same graduate program, and so have a lot in common that revolve around what we’re studying, but recently its been very full on so neither of us want conversation to purely revolve around it.
When we first got together it was pretty intense – after 2 weeks I had to leave to have an operation, and he was wonderful while I was away for 5 weeks – wrote me romantic letters, rang me all the time.
I know that the dynamic is going to change, but I’ve only ever been in really unhappy relationships before that never progressed so I’m not used to this. And I’m now consumed by the fear that we’ll break up over the 4 month summer period when we can’t afford to be together, particularly because due to our tiredness and lack of money to do things conversation topics are becoming thin on the ground.
Also despite us being very close and him being very loving, he hasn’t actually SAID that he loves me yet, and so I’m too scared to tell him how I feel.

I was just wondering if anyone had any advice. I’m worried that I’m worrying about a problem that I’m creating out of nothing. He’s still very sweet and attentive, but being a graduate program the last few months have been very stressful for both of us. I don’t want to convince myself that there’s a problem if there isn’t one.