Present perfect means the action was completed before the present time. Present perfect includes actions that happened at an unspecified time before the present.
I have loved him before means that I loved him at an unspecified time before the present. I loved him sometime before now. You do not know when I loved him, just that I loved him in the past. The action is complete and I do not love him anymore, but I could possibly love him again.
I have loved him before. I might love him in the future.
Simple past shows an action that happened in the past. It does not give any other information. It simply states a fact. That is why it is called "simple."
I loved him means that I loved him in the past. There is not a specified time, but the time period is usually understood from context.
I loved him yesterday/last year/when we were married…