Under grace, is God's forgiveness conditional on whether I forgive other people?

Under grace, God's forgiveness is not conditional on whether you forgive other people. The Law required forgiving others before being forgiven, but grace shows God forgave you whether you forgave your neighbor or not. Ephesians 4:32 presents this contrast, so forgiveness is not earned by first forgiving others.

Les explains that under Law, a person could not be forgiven until he had forgiven the other person; that is what Law demanded. The religious gentleman described this mindset: I have to forgive them, because if I don't, I can't be forgiven by God. But Ephesians 4:32 is written by the Apostle of Grace, the one who said in Romans that believers are not under Law but under Grace. Les emphasizes that grace asks, whether I forgave my neighbor or not, what did God do for me? He forgave me. So grace makes clear that God's forgiveness is not conditioned on our first forgiving others.

Ephesians 4:32

And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ’s sake hath forgiven you.

Under Grace, is your forgiveness by God conditional on forgiving your neighbor?

No. Under Grace, God's forgiveness is not conditional on first forgiving your neighbor. The Law demanded forgiveness of others before forgiveness from God, but the Apostle of Grace writes that God forgave us whether or not we forgave our neighbor (Ephesians 4:32).