Let's not forget that Tifa actually dissaproves of Cloud's delivery service. Yes, she doesn't like him doing the delivery service. Why? Because it takes him away for long periods of time. It annoys her.

She supported him running it at first, but soon it takes its toll on her.

After Cloud started his delivery service, their "family" life changed greatly. It wasn't too good. Besides morning and late night, Cloud was usually not at home. And of course, there were less chances for the three of them to have conversations together. Tifa closed the bar for a day during the week but it didn't stop Cloud from his job. It wasn't hard for Cloud to turn down requests. I just wanted us to be able to take a day off together now and then but, I suppressed that selfishness in me.
Tifa forced herself to talk to Cloud. When Marlene was near, she would pick something positive, something that wouldn't turn the conversation into a serious matter. Cloud was bewildered at the way Tifa changed but guessing at what she was doing, he went along with the mood and talked to her.
If it wasn't incompability, why would even Tifa herself, who supposedly loves Cloud, have to 'force herself' to talk to him, only when the children are around? Not only that, Cloud senses their incompability and doesn't make it up to Tifa. Instead, he just casually plays along with her little fake conversations when the children are around, otherwise, not talking to he at all.

Does that seem like a healthy, compatible relationship to you?

No, I do not see this has anything to do with guilt or depression. I think that Cloud will not move on with Tifa, especially since it is so hard for them to tolerate each other's perfectly opposites way of living.