We will need a video of yourself playing in order for us to make any meaningful comments.
I have friends who play more tennis than ping pong, and they also seem to like to defend, so I understand your favoritism. (They just like to hit the ball late, at least, that what I observe.)
If you want to learn how to defend well, you are going to have to find a training partner that attacks well. There's not much more I can say without seeing, and I don't want to assume.
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If I do assume:
You probably back off the table a lot.
If you do that, you won't really be able to block and will have to start lobbing. So, I'll suggest learning how to stand your ground and block. Block to the corners, learn how to block softly, and block hard. You have to learn how to absorb the impact, and learn to redirect it.
You are probably decent at lobbing. Good lobs are high and deep on to the table. Adding topspin to the lob is great. You can do this by simply lobbing when the ball drops to about your waist and hitting it high up. A little wrist action is optional, and great for adding sidespin.
Good pushes are essential. Low, deep, and fast ones are ideal.
Service return is crucial. Make sure you learn to handle every serve in a least 4 different ways. Either by drop shot, pushing, looping, and flipping.
Make sure you can handle openers: such as flips and loops.
You say you have a strong forehand. Modern defenders nowadays must have strong forehand counterattacks. Practice counterattacking. A very big advantage about being a defender is that the opponent doesn't know when the defender will attack.
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If you ever feel that you are somehow trapped in a corner while playing, you aren't being a good defender. Being a good defender is about having many options to deal a shot, in order to mix up the opponent. If you have no options left, or if you start getting repetitive, it's about time you learn a few.
It is very difficult being a defender because there is much more you need to learn. You need to have a larger skillset than most players. So, don't give up.