I think we can get into the habit of not wanting others to feel the impact of 'deep upset' and when this is the case it kind of becomes a matter of 'Doesn't matter how I'm feeling life or this situation, as long as the other person doesn't feel any deeply confronting emotion. That's the main thing'. A deeply compassionate person will not want others experiencing emotional pain. It's in their nature. It kind of becomes about us taking responsibility for everyone's feelings. You can become kind of like protector of sorts. That's a tremendous amount of responsibility at times, protecting everyone around you. Can be exhausting. I've found it's so much easier dealing with unfeeling or insensitive people. Such people feel little, so you don't have to worry yourself so much.
I think in the case of ending a relationship early on, perhaps the question comes down to 'Do I want them to feel long term pain or short term pain, out of the 2?'. Of course, being a sensitive guy, I imagine your answer would be short term pain, which means not dragging things out. If you prefer no pain at all, unfortunately we don't always have that choice. Instead, sometimes we're left to choose only out of painful choices. Such a choice is tough when you're a thoughtful sensitive person and you can easily get a sense of what that other person will be left to feel. Can be so hard, feeling for others.
I wish there was far more talk about 'feelings' when we were growing up. They're so important, so significant. Little is ever spoken of them, typically. Feeling connections to people, disconnections, gut feeling/instinctive feeling, feeling 'overwhelm', feeling peace, feeling whether we're on the right track and so on, there's just so much to them. I think if we were better educated growing up, we wouldn't be left with so many questions about them, such as 'How do I calm myself down while feeling a nervous system in hyper drive?'.
I think, in order to master feelings we have to begin seriously questioning them, which is exactly what you've been doing, which helps explain why it's all felt so incredibly serious. To basically question 'feelings' doesn't have such a serious feel to it. If you were to ask people who've experienced serious questioning, many of them would say 'It's such a confronting and sometimes horrible process, getting through the questioning stage'. Of course, it's the answers you find that help put you in the league of masters when in comes to emotional mastery :)