How do I speak when I get easily emotional

I have a problem of pushing down my feelings and never addressing it. This time I messed up and I have to say sorry to the person. I genuinely want to explain everything that's going on and apologize but I find it hard.

Even if it's an old problem that I haven't thought about for years, just the thought of opening my mouth to say anything about it makes me cry. In the end, I just cry and choke on my tears and can barely say anything comprehensible and instead sound like a toddler having a tantrum. That is why I rarely to never open up to someone because that's all I end up doing, just sob into such a mess.

Help me.