Any tendencies within your lover toward emotional displays or instability are only heightened by this relationship. What they need is a grounding influence, a certain level of support, nurturing and sensitivity -- and unfortunately, they're not likely to get that from you, unless other aspects between you support a more stabilizing influence. You find that you relate to them erratically -- one minute you think yourself in love as you experience intense feelings of togetherness, but then something you say hits a sensitive button deep inside them, one of insecurity or hidden anger, and then the proverbial you-know-what hits the fan!
Granted, this can be pretty exciting; those lows you inspire in each other only serve to make the highs feel that much more intense and heady. The problem is, you don't know how to stop hitting your lover's buttons. Something between you just inspires this kind of touchiness that doesn't do much for any overall feeling of trust or intimacy. In order to make it work, your partner, especially, has to allow for plenty of space within the relationship, if for no other reason than to provide some cool-off time for those moments when you set each other off. Space can lead to feelings of loneliness in them, and in the end, they might end up deciding that a close romantic relationship just isn't possible with you, and that a friendship better suits the two of you.