Watermelon can give me some problems because of the fiber in it. But, I can eat a small piece and, when I'm chewing, if it's fibrous, I will spit the fiber part out but still enjoy the flavor and juice. Sometimes a bite isn't really fibrous and I can eat it just fine. Just try a little and see how you go. Ice cold watermelon is so good in the summer.
I've had my ostomy for 24 years. I eat mostly strawberries, a few grapes and cherries at a time. Bananas constipate me. I love raspberries and blackberries but the seeds cause me problems so I don't get them. I can enjoy their flavor in jams. I don't know why the seeds in strawberries are fine for me. Pineapple can be fibrous, too, so I again can't eat much of it but a bite or two seems to be fine and I always spit out anything that is chewy...even the "skin" of blueberries, etc. But that's me. How foods affect us can be different. I do enjoy pears but if the skin is thick I spit that out, too. Same with peaches and nectarines. Obviously, I only eat some fruits at home.
I hope this helps you.