Teach me thy way, O LORD; I will walk in thy truth: unite my heart to fear thy name.
Psalm 86:11 · KJV
'Unite my heart' is an unusual prayer, and once you have heard it you notice how badly you need it. David is not asking for more willpower. He is asking to be made one thing.
A divided heart is not half-hearted. It is fully committed to two incompatible things at once, which is why it exhausts you. It is being genuinely glad for someone and quietly resentful in the same breath. It is worshipping sincerely on Sunday and negotiating with the same sin on Tuesday.
Notice that unity is something God does, not something you achieve. 'Unite my heart' is a request, not a resolution. Resolutions divide the heart further; surrender is what makes it one.
Name the two things your heart is currently divided between. Say them out loud to God. Do not resolve to do better — ask Him to unite you.