Spending time with people we are having a hard time loving has an uncanny way of helping our hearts to come around. I am amazed how it works almost every time with me. It seems like there's always someone that I'm tempted to harbor bitterness against. On my best days, I cry out to God to not let me hold onto those feelings. When I'm thinking rightly, I remember that I'm not perfect either. But, even in those moments, I often feel helpless, and struggle to see anything besides the failings of that person. That's where the secret of spending time with them comes in. It's really hard to stay mad at someone you are spending time befriending.
People are Needy
There have been people that I've struggled to love for various reasons for even years at a time, only to find that when I attempt to talk to them like a friend, and just know them, there is a lot more to them as a person than the glaring problem I'd been fixated on. People have reasons for the way they act. That doesn't excuse sin, but it does cause our hearts to soften a bit when we realize someone is acting poorly because of a subconscious need that hasn't been met in their own heart. Grace is so important when it comes to being able to love people well. People are needy. If we find ourselves only able to connect with a few people as friends, it might be time to step back and evaluate if we are even giving those that are hard to love a chance to be loved, despite their weaknesses.
Disagreements are often what keep us from wanting to spend time with each other. If we're honest, we'll realize there isn't a single person on this earth that we wouldn't disagree with about something, but some issues do cut us personally deeper than others. Those are usually the people that we avoid. But avoiding someone you disagree with only makes the rift broader. I'm not saying spending time with people makes us all think alike; I just think it causes us to care. Do you have a friend that has gone astray? Don't ignore them until they come back. Spend time with them, so that you can love them well, and they will also be forced to still care for you, and not just write you off as someone that doesn't understand.
Bitterness is too easy to hang onto from a distance. Confront how you're feeling and do exactly what you don't feel like doing: spend time with that person and attempt to be their friend. Forgiveness and soft-heartedness generally follows.
"Be kind to one another, tender-hearted, forgiving each other, just as God in Christ also has forgiven you." -Ephesians 4:32